Treatment of industrial wastewater streams presents numerous difficult challenges, including efficient and effective degradation of dissolved compounds or ions and/or organic materials, with minimum investment, and with minimum interference with industrial efficiency and output. In other words, the treatments which are often mandated by government statute or regulation need to make effective use of energy, manpower, capital and other resources, while returning wastewater to be disposed of or recycled containing acceptable amounts of contaminants.
U.S. Pat. No. 5,470,559, issued Nov. 28, 1995 (Grolman et al.), assigned to the same assignee as the present application, discloses a method and apparatus for recycling used linings of aluminum reduction cells, more commonly called spent potlinings (SPL). The potlinings, composed primarily of carbon, refractory brick, and cryolite, include fluorine, alumina and sodium, along with free and complexed cyanides. The process involves grinding the spent potlining material to a powder, and treating the powder with aqueous sodium hydroxide to produce a slurry. The slurry is separated into solids and liquid; the liquid is then diluted (if necessary) to produce a solution containing the cyanide or complexed cyanide ions suitable for cyanide destruction and sodium fluoride crystallization.
U.S. Pat. No. 5,160,637, issued Nov. 3, 1992 (Bell et al.), also assigned to the same assignee as the present application, discloses a method and apparatus for treatment and degradation of cyanides and ferrocyanides contained in wastewater resulting from the conversion of alumina into aluminum metal. The patent discloses a vertical tubular reactor in which the wastewater is treated under heat and pressure. In some applications, cyanide and ferrocyanide ions can be effectively degraded using high pressures and temperatures as disclosed in that patent. The equipment necessary to carry out the process, however, is quite expensive to purchase and install, and uses considerable amounts of energy to produce the temperatures and pressures useful therein. Accordingly, a less expensive system for accomplishing that goal would be desirable.
European patent application 469 737 A2 published on Feb. 5, 1992 in the name of Tioxide Group Services Limited discloses a destruction process in which chemical waste is burned in oxygen using an electric plasma flame to heat a stream of gas which contains at least 70% by weight oxygen. Liquid waste in fine droplet form is introduced into the gas stream via a two-fluid atomiser.
U.S. Pat. No. 3,051,639, which issued on Aug. 28, 1962 and was assigned to Union Carbide Corporation, discloses a process and apparatus for carrying out chemical reactions, particularly the conversion of liquid or gaseous hydrocarbons into acetylene. The process involves creating a stream of hot arc gas from a wall-stabilized electric arc and injecting a gaseous or liquid hydrocarbon is injected into the stream, or the stream is directed into a relatively large volume of liquid hydrocarbon.
U.S. Pat. No. 4,438,706, which issued on Mar. 27, 1984 and was assigned to Villamosipari Kutato Intezet, discloses a procedure and equipment for destroying fluid waste containing vaporizable organic materia by a plasma technique. The procedure involves producing a plasma, creating a plasma torch at one end of a reactor, introducing the waste in vapour form and oxygen into the torch for interaction with the reactor and discharging end products from the reactor. The reactor is a double-walled tube, the inner wall being perforated to allow the passage of air into the reaction zone.
German patent DE 44 40 813 A1, which was published on May 18, 1995 and was assigned to Fraunhofer-Gesellschaft zur Forderung der angewandten Forschng e.V., discloses a method for the treatment of liquids, including liquids containing cyanide. The liquid is held in a discharge zone between two opposed electrodes supplied with alternating current. Micro discharge filaments are formed in the discharge zone extending from the liquid surface to the opposing electrode. The method destroys hazardous matter in the waste water and converts it into harmless compounds.